GB2230208A

GB2230208A - Transformers

Info

Publication number: GB2230208A
Application number: GB9004494A
Authority: GB
Inventors: Yoshiki Aosaki
Original assignee: Sanken Electric Co Ltd
Current assignee: Sanken Electric Co Ltd
Priority date: 1989-03-01
Filing date: 1990-02-28
Publication date: 1990-10-17
Anticipated expiration: 2010-02-28
Also published as: GB2230208B; DE4006697A1; GB9004494D0; JPH0325219U

Description

1 Title: Transformers

DESCRIPTION

The present invention relates to a transformer and, in particular, to a transformer of small size for 5 use in high frequency operation.

Transformers have been utilized to convert a DC input rectified from the power voltage (AC 10OV or 20OV) into DC output voltage (DC 5V or 12V). Such transformers comprise primary and secondary windings in a sufficiently insulated structure. For instance, as schematically shown in Figure 7 of the accompanying drawings, a prior art transformer comprises primary windings 1 and 11, a secondary winding 2, a bobbin 3 provided with a hole 4, a core 5 disposed within the hole 4, barriers 6 and insulating papers 7. The primary windings 1, 11 and secondary winding 2 are wound on the bobbin 3 in overlapped relation to provide an intimate electromagnetic coupling among these windings. The insulating papers 7 serve to provide a required insulation between the primary and secondary windings 1 and 2 and between the secondary and primary windings 2.and 11. Provided adjacent to flanges 3a, 3b of the bobbin 3 are insulating barriers 6 which are effective to increase a creepage distance between the primary and 2 secondary windings. Figure 8 of the accompanying drawings schematically exhibits an example of the transformer circuits wherein the primary and secondary windings 1, 11 and 2 respectively have terminals la, 1' 5 and 2 respectively have terminals la, lta and 2a.

Figures 9 and 10 of the accompanying show an exemplified appearance of a prior art transformer wherein each extension of the primary and secondary windings 1, 11 and 2 is connected with a corresponding terminal conductor 9 secured on an upper flange 3a of the bobbin 3. These extensions adjacent to the terminals la, lla and 2a are covered with insulating tubes 8 and secured to the terminal conductors 9 through grooves formed on the upper flange 3a.

Most of the prior art transformers need the barriers 6, insulating papers 7 and insulating tubes 8 for electrical insulation between the primary and secondary windings 1 and 2 and between the secondary and primary windings 2 and 11. Such windings 1, 1f and 2 are generally coated with enamel (notshown), exclusively in order to maintain a low insulation inside each layer of the primary or secondary winding 1, it or_ 2, without consideration of insulation between the primary and secondary windings. Accordingly, prior art transformers have required the above-mentioned insulating structure including the insulating barriers, 1 3 papers and tubes.

According to Section 380 of IEC (International Electrotechnical Commission), the insulation structure requires more than three sheets of insulating paper 7 positioned between the primary and secondary windings 1, 2 and between the secondary and primary windings 2 and 1r, provided that two sheets of insulating paper 7 can resist an applied voltage of 3,750 V. In addition, under the regulation of the Section, more than 6 mm of creepage space distance must be provided between the primary and secondary windings 1 and 2 and the secondary windings 2 and 10. However, such structure obviously needs a larger space for positioning the barriers 6 and insulating papers 7 so that it would be difficult to is produce a small-sized transformer for high frequency operation. Another disadvantage of such structure is that arrangement of the insulating barriers 6 and papers 7 reduces the coupling performance of the magnetic circuits formed by the windings.

Also, as understood from Figures 9 and 10, assembling of the transformers requires insertion of end terminals la, 2a and lla of the primary and secondary.

windings 1, 2 and 11 into insulating tubes 8, and thereafter these terminals must be connected with the terminal conductors 9 of bobbin 3. Apparently, these processes are troublesome and time-consuming and also 4 require skills.

An object of the present invention is to provide a small-sized transformer for high frequency operation.

According to the instant invention, a transformer is provided which comprises primary and secondary windings wound around a core in an overlapped relation, at least one of the primary and secondary windings having a conductor coated with a coating formed of insulating plastics material selected from polyethylene, polyethylene terephthalate, polyimide, polyester, polyether, polyacetal, polyvinyl formal, polyurethane and epoxy resin.

The coating may comprise a.plurality of layers formed of the insulating plastic materials. In a is preferred embodiment of the invention, the primary and secondary windings are wound substantially across the whole width between two flanges of a bobbin.

In the transformer according to the present invention, insulation of the primary and secondary windings is made by the insulating coating covering the conductor of each winding. Also, as theprimary and secondary windings may be intimately wound around the_ core in overlapped relation without insulating barriers -and papers, the transformer may be made in small size.

Furthermore, each end terminal of the windings may be easily attached to the terminal conductors of the bobbin n 1.

without the insulating tube into which each end portion of the windings is inserted.

The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 shows a schematic section of a transformer according to the present invention with three windings; Figure 2 is a perspective view partly indicating one of the windings used in the transformer of Figure 1; Figure 3 is an elevation view of a bobbin on which the windings of Figure 2 are wound; Figure 4 is a side view of Figure 3; Figures 5(A) and 5(B) show practical size of cores according to an embodiment of the invention and prior art; Figures 6(A) and 6(B) are schematic sections indicating respectively sizes of the invention's and prior art transformers; 20 Figure 7 is a schematic section of a-prior art transformer; Figure 8 is a circuit utilized by the invention's transformer; Figure 9 shows an elevation view of a bobbin on which the windings are wound in a prior art method; and

Figure 10 is a side view of Figure 9.

6 A preferred embodiment of the present invention will be described hereinafter in connection with Figures 1 to 6 of the accompanying drawings which include the same reference symbols as those shown in Figures 7 to 10 to indicate the same parts or portions, and explanation thereon is omitted.

As shown in Figure 2, each of the primary and secondary windings, 1, if and 2 comprises a conductor 10 and an insulating coating 11 coated on the conductor 10.

The coating 11 includes a first layer 11a closely secured to the conductor 10, a second layer 11b covering the first layer 11a, and a third layer 11c covering the second layer 11b. Each of these layers Ila, 11b and 11c is formed of insulating plastic material selected from is polyethylene, polyethylene terephthalate, polyimide, polyester, polyether, polyacetal, polyvinyl formal, polyurethane and epoxy resin. Even when any breakdown in insulation is produced in one of these layers which form a plural- or multi-layered structure, the remaining layers ensure full insulation for any necessary voltage level.

The first to third layers 11a, 11b and Ilc may be formed by vacuumdepositing different insulating materials in turn on the conductor 10, dipping it in fluid insulating materials, or winding adhesive insulating film strips around the conductor 10.

_k Otherwise, svnthetic 7 the coating may resin tanes on be formed by winding the conductor 10 and subsequently heat-sealing the tapes without an adhesive agent. The thickness of the coating 11 for each winding 1, 10 and 2, is desirably less than 0.05mm in view of workability, insulating characteristics and minimizing size of the transformer. For example, if the first layer of polyester film shown in Figure 2 has a thickness of 0.012mm and each of the second and third layers has a thickness 0.004mm, the coatings between the primary and secondary windings can resist a voltage over 8 kv. In this case, it is advisable to utilize materials of gradually low melting points from the first to third layer 11a - 11c, as the first inner layer 11a closest to the conductor 10 would be subjected to an elevated temperature higher than that of the outer layers when the conductor 10 is energized.

To assemble the transformer, the primary windings 1, 11 and the secondary windings 2 are wound around the bobbin 3 substantially across the whole width thereof without insulating barriers and papers in order of the primary windings 1, the secondary winding 2 and then the primary winding 11. Utilization of the bobbin 3 around.which these windings are wound, may prevent collapse of the wound windings and facilitate attachment and connection of the windings. When the windings have a 8 smaller number of turns, it is preferred to wind the turns at wider intervals throughout the whole width of the bobbin. Also, as shown in Figures 3 and 4, the terminals la, 1af and 2a may be attached to terminals 9 by soldering them without the insulating tube 8.

Figures 5 and 6 show comparative practical size of shell type transformers according to the instant invention and the prior art wherein the primary windings 1 and 1f respectively have conductors 10 of outer diameter 0.4mm, 0.5mm and number of turns 60, 36, and the secondary winding 2 has a conductor 10 of outer diameter 0.8mm and number of turns 24. Figures 5(A) and (B) show the size of cores employed in the transformer of the present invention and in the prior art. Figures 6(A) and (B) show each section of the transformer of the invention and the prior art to indicate each coil size in millimeters. Whereas the prior art transformer has a volume of 37.52cm and weight of 90 g. the transformer of the invention has a 20 volume of 27.17cm and weight of 75 g, and therefore is smaller by approximately 28% in volume and lighter by approximately 16% in weight in comparing with theformer. The foregoing embodiment may further be altered. Insulating papers may be inserted between the primary and secondary windings 1 and 2 and between the secondary

9 and primary windings 2 and 11 wound around the bobbin 3 shown in Figure 1 to form even surfaces on corrugated outer surfaces of the turns in compensation of the corrugation for easy winding operation. In this case, a smaller number of or a variety of insulating papers may be selected, since the insulation of the windings is not dependent on the insulating papers 7. In addition, these windings may be wound directly on the core without the bobbin 8. Also, the primary and secondary windings may be formed into bifilar winding type to provide a higher coupling performance in the magnetic circuits. The transformer may be of the core or troidal type or other type instead of the.shell type.

Since the transformer of the present invention can keep full insulation between the primary and secondary windings without insulating barriers, papers and tubes which are necessary for prior art transformers, it may be made in a smaller size particularly for use in high frequency operation through the simplified assembly process. If it is used in a frequency range of 500 KHz to 1 MHz, the volume of the transformer can be reduced to one- half to two-thirds of. that of prior art transformers. Moreover, the coupling performance in the magnetic circuit formed by the windings can be remarkably improved.

Claims

1. A transformer comprising primary and secondary windings wound around a core in an overlapped relation, at least one of the primary and secondary windings having a conductor coated with a coating formed of insulating plastics material selected from polyethylene, polyethylene terephthalate, polyimide, polyester, polyether, polyacetal, polyvinvyl formal, polyurethane and epoxy resin.

2. A transformer as claimed in claim 1, wherein said coating comprises a plurality of layers formed of the insulating plastic materials.

3. A transformer as claimed in claim 1 or 2, wherein the primary and secondary windings are wound substantially across the whole width between two flanges of a bobbin.

4. A transformer comprising primary and secondary windings wound around a core in an overlapped relation in which at least one of the primary and secondary windings has a conductor coated with an insulating coating which comprises a plurality of layers.

5. A transformer as claimed in claim 4, wherein at.least one of said layers is of insulating plastics material selected from polyethylene, polyethylene terephthalate, polyimide, polyester, polyether, t 111 11 polyvinyl formal, polyurethane and epoxy polyacetal, resin.

6. A transformer substantially as hereinbefore described with reference to and as illustrated in any one of Figures 1 to 4, 5A, 6A and 8.

Ped 1990atThe PatentOM0e,61&t4e HOUACA6?1 Rgh Holborn. London WC1R 4TP. Purther COPICA InaY bt obed&om ThPatentozice